A conventional heat-curable antifogging agent composition using a random copolymer has an insufficient adhesion property with respect to a plastic or a glass base material. The present inventors disclosed a heat-curable antifogging agent composition with an improved adhesion property in the Japanese Laid-Open Patent Publication Nos. Hei 6-212146 and Hei 6-107967. In the case of forming a coating film with the antifogging agent composition, in order to obtain a hardened coating film with a good performance, strict process conditions of a high temperature of 120° C. or more and a hardening time of 30 minutes or more are required. Since the obtained coating film is provided with the hydrophilic property on the coating film surface by a hydrophilic polymer part in a block or grafted copolymer, and at the same time, the adhesion property with respect to the base material can be provided by a hydrophobic polymer part, it is excellent in terms of both the hydrophilic property and the adhesion property. Furthermore, since a surfactant contained in the coating film lowers the surface tension of water drops adhered on the coating film surface so as to make a water film out of the adhered water drops, the coating film has the excellent antifogging property.
Recently, for energy conservation and productivity improvement in coating equipment, lowering of the drying temperature for an antifogging agent composition and reduction in the drying time are important. Therefore, by lowering the hardening temperature of the heat-curable antifogging agent composition or by reducing the hardening time, the composition may be hardened insufficiently so that a problem arises in that the water resistance of the coating film is lowered.
By adding an acid hardening catalyst used in a heat-curable paint such as an acrylic melamine paint or an alkyd melamine paint in the heat-curable antifogging agent composition, lowering of the hardening temperature and reduction in the hardening time can be achieved. However, at the time the water film is formed on the surface of the antifogging coating film after hardening and the water runs down so as to be dried, a problem arises in terms of the external appearance in that the trace of the running water is conspicuous as pollution.
In the case where the antifogging coating film is formed on, for example, the inner surface of a meter cover or a light cover, it is difficult to wipe off the pollution of the running water trace due to the structure of the meter or the light. Therefore, an antifogging coating film without the risk of generating the running water trace is called for.